High-temperature ovens, called reactors, are used to create structures of very fine dimensions, such as integrated circuits on semiconductor substrates. One or more substrates, such as silicon wafers, are placed on a substrate support inside the reaction chamber. Both the substrate and support are heated to a desired temperature. In a typical substrate treatment step, reactant gases (also referred to as precursors) are passed over the heated substrate, causing the deposition (e.g., chemical vapor deposition, or CVD) of a thin layer on the substrate. CVD is typically conducted at high temperatures, such as 250-900° C.
Deposition equipment normally includes a system for delivering gas to the reaction chamber. The gas delivery system typically comprises a plurality of precursor sources, optionally one carrier gas and/or purge gas source, a network of pipes for delivering the precursor gases to the reaction chamber, eventually an injection manifold or showerhead for injecting the gas evenly into the chamber, and a number of valves for controlling the gas flow. Also, some precursor sources may be in powder or liquid form, and means for vaporizing such precursors can be provided (e.g., bubblers).
Another type of deposition process is atomic layer deposition (ALD). In ALD, two complementary precursors are alternatively introduced into the reaction chamber. Typically, a first precursor will adsorb onto the substrate surface, but it cannot completely decompose without the second precursor. The first precursor adsorbs until it saturates the substrate surface; further growth cannot occur until the second precursor is introduced. Thus, the film thickness is controlled by the number of precursor injection cycles rather than the deposition time, as is the case for conventional CVD processes. Accordingly, ALD allows for extremely precise control of film thickness and uniformity. ALD is typically conducted at temperatures in a range 250-500° C.
In ALD, the reaction chamber is typically pulsed with a non-reactive protective gas between injections of the two precursor gases, in an attempt to rid the chamber of any excess of the preceding precursor gas. Otherwise, the excess preceding precursor would intermix and react with the subsequently pulsed precursor to form unwanted CVD-type growth on the substrate surface and/or on surfaces of the chamber.
For various reasons, including low electrical resistivity, good thermal stability, and good diffusion barrier properties, there are numerous applications for titanium nitride (TiN) in the fabrication of integrated circuits. Exemplary applications include use as a contact or barrier layer and as an electrode in electrical devices, such as transistors.
The properties of TiN, however, are closely dependent on processing and deposition parameters. Thus, the suitability and desirability of deposited TiN for a particular application can depend on the availability of a deposition process able to form TiN with desired properties, e.g., high uniformity and low resistivity. As a result, research into the development of new TiN deposition processes is on-going.
For example, the Low Pressure Chemical Vapor Deposition (LPCVD) of TiN films in a hot wall furnace has been described by N. Ramanuja et al. in Materials Letters, Vol. 57 (2002), pp. 261-269. The reach of Ramanuja et al. is limited, however, as Ramanuja et al. investigated 100 mm wafers, rather than industry standard 200 mm and 300 mm wafers.
In addition to being able to form acceptable TiN films, it is desirable for the deposition temperature of the TiN deposition process to be relatively low, thereby increasing flexibility for integrating the deposition process with other processes and structures. For example, reducing deposition temperatures to the 400-500° C. range allows the films to be used in conjunction with multi-level aluminum or copper metallization.
It has been found, however, that a reduction in the deposition temperature results in the incorporation of significant amounts of chlorine in the TiN film and results in a substantial increase in resistivity, which is undesirable. See J. T. Hillman, Microelectronic Engineering, Vol. 19 (1992), pp. 375-378. To reduce the resistivity and the chlorine content of the film, Hilman discloses a single wafer deposition process followed by a post-deposition anneal. Undesirably, however, such a process requires an additional process step and also limits throughput by using single wafer processing.